Flue gases from combustion installations, such as power plants or waste incineration plants, contain a number of pollutants, which must be removed from the flue gas before they are released to the environment. Modern combustion installations are equipped with flue gas cleaning devices, which remove sulfur dioxide, nitrogen oxides, hydrogen halides and entrained ash contained in the flue gas.
In addition to the pollutants referred to above, the flue gas contains traces of heavy metals, which must be removed from the flue gases due to their toxicity. One particularly poisonous heavy metal contained in the flue gas is mercury. This is washed out of the flue gas in conventional wet flue gas desulfurization (FGD) plants and flows with the waste water from the FGD into the FGD waste water treatment (WWT) plant. The mercury dissolved in the FGD waste water is precipitated in the WWT in a low-solubility form together with other solid materials in the form of FGD-WWT sludge. As a result of the contamination with mercury, this FGD-WWT sludge can, however, not be burned but must be disposed of as hazardous waste.
European application EP 0 792 186 B1 discloses a cleaning method of flue gases, with which mercury can be removed from the flue gases. For this purpose, the flue gases are subjected to a wet scrubbing process, wherein this wet scrubbing process is conducted with the addition of activated carbon particles, which adsorb the heavy metals and, in particular, mercury. The activated carbon particles are then separated from the suspension produced in the wet scrubbing process and recirculated into the wet scrubbing process, whereby a fraction of the particles is tapped off and thermally desorbed. The thermal desorption is complex in regards of process technology and is thus expensive.